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While incidence rates remained stable throughout the study period, incidence rates in females increased 3% per year between 2000 and 2017. The increase was seen primarily in women 40-49 and 50-59.
During the last 5 decades, general incidence of psoriatic arthritis (PsA) has remained stable. However, an increasing percentage of female patients have developed the condition, according to a population-based study published in Arthritis and Rheumatology.1
“There is disparity in the proportion of male and females,” explain investigators. “The difference in incidence and prevalence estimates across different geographic regions could be due to different data collection periods, underdiagnoses (in Asia), or genetic and environmental differences… higher prevalence of obesity, hyperlipidemia, and smoking, which are strong risk factors for PsA, could account for higher prevalence of PsA in North America.”
In the retrospective study of patients with PsA in Olmstead County, Minnesota, investigators analyzed the annual incidence of PsA from 2000-2017 and assessed time trends of incidence and mortality rates between 1970-2017. They used data from the Rochester Epidemiology Project (REP). Medical records used included the Mayo Clinic, the Olmsted Medical Center, nursing homes, and private practitioners.
Eligible patients were ≥18 years who met ClASsification of Psoriatic ARthritis (CASPAR) criteria, the date of which was considered to be the incidence date. ICD-9/10 diagnostic codes allowed investigators to screen for patients with PsA. Additional information was recorded including demographics and clinical characteristics. Incidence rates were adjusted for age and sex of the patients, based on the 2010 white population in the United States. Mortality rates in patients with PsA were compared with survival rates of the white population in Minnesota.
Of the 484 patients with PsA, 164 were aged ≥18 years with validated CASPAR criteria between January 1, 2000 and December 31, 2017. The patient population had a mean age of 46.4 (±12.0) years, 53% were male, and 87% were white. Throughout the course of the study, 39% were female in 1970-1999, which increased to 41% in 2000-2009, and 54% in 2010-2017. As predicted, incidence of PsA between the years of 2000-2017 was 8.5 (95% CI 7.2-9.8), and higher in the male cohort (9.3) than the female cohort (7.7). At diagnosis, 150 (91%) of patients had active psoriasis and 7 (4%) had a history of psoriasis.
Incidence rates remained generally stable throughout the study period, with an increase in PsA of 4% a year during 1970-1999. There were no differences in the sexes during that time period. However, between 2000-2017, incidence rates in females increased 3% per year. The increase was seen primarily in women 40-49 and 50-59.
As far as mortality, during a median 13-year follow-up between 1970-2017, 40 patients with PsA died. However, survival rates were the same as the general population and no changes over time were observed.
The study was strengthened by the defined geographical population and the use of REP in conjunction with CASPAR criteria. Additionally, the wide gap of years that patients were studied helped investigators to determine trends in PsA in the same population setting.
Limitations included the possibility of missed and misclassified cases of mild PsA, as well as those who never sought treatment with a rheumatologist. Further, asymptomatic patients may not have been required to have axial radiographs performed, which could contribute to an under-represented patient population. The population of Olmsted County is ~90% white, thus possibly limiting generalizability across other ethnic populations. Finally, as always, a retrospective study depends on medical record documentation, which may not be completely accurate.
“Our study found stable incidence of PsA in recent years. However, an increasing proportion of females was found in this study,” concluded investigators. “Further work is needed to determine the role of sex hormones, gene expression and other mechanisms underlying these changes.”
Karmacharya P, Crowson CS, Bekele D, et al. The Epidemiology of Psoriatic Arthritis over 5 Decades: A Population-Based Study [published online ahead of print, 2021 Mar 28]. Arthritis Rheumatol. 2021;10.1002/art.41741. doi:10.1002/art.41741